1. Field of the Invention
The present invention relates to an efuse structure, and particularly to a contact efuse structure used for semiconductor devices and methods of making a contact efuse device and making a read only memory (ROM).
2. Description of the Prior Art
As semiconductor processes become smaller and more complex, semiconductor components are influenced by impurities more easily. If a single metal link, a diode, or a MOS is broken down, the whole chip will be unusable. To treat this problem, fuses can be selectively blown for increasing the yield of IC manufacturing.
In general, fused circuits are redundant circuits of an IC. When defects are found in the circuit, fuses can be selectively blown for repairing or replacing defective circuits. Besides, fuses provide the function of programming circuits for various customized functions. Fuses are classified into two categories based on their operation: thermal fuse and efuse. Thermal fuses can be cut by lasers and be linked by laser repair. An efuse utilizes electro-migration for both forming open circuits and for repairing.
Opening for a poly efuse when it is blown happens at a polysilicon layer thereof. A blowing mechanism of efuse is typically shown in FIG. 1. The cathode of an efuse structure 1 is electrically connected to the drain of the transistor as a blowing device 2 (or referred to be as a driver). Voltages Vfs, Vg, and Vd are applied to the anode of the efuse structure 1, the gate of the transistor, and the drain of the transistor, respectively. The source of the transistor is grounded. The electric current is from the anode of the efuse structure 1 to the cathode of the efuse structure 1; and the electrons flow from the cathode of the efuse structure 1 to the anode of the efuse structure 1. The electric current suitable for the blowing is in a proper range. If the electric current is too low, the electron-migration is not completed, and if it is too high, the efuse tends to be thermally ruptured. In general, the blowing current for an efuse structure made by a 65 nm manufacturing process is about 13 mA.
FIGS. 2 and 3 illustrate a conventional poly efuse structure. The poly efuse structure 10 has a neck portion and includes an anode 12, a cathode 14, and a fuse body 16. A plurality of tungsten contacts 18 are disposed on the anode 12, and a plurality of tungsten contacts 20 are disposed on the cathode 14. As shown in FIG. 3, the anode 12, the cathode 14, and the fuse body 16 include a polysilicon layer 22 and a metal silicide layer 24 on the polysilicon layer 22. The metal silicide 24 assists a better electrical contact between the tungsten contacts and the electrodes. A sufficient electron flow must be supplied to the cathode 14 through the plurality of the tungsten contacts 18 disposed on the cathode 14 and flow into the polysilicon layer 22 and the metal silicide layer 24 of the neck-shaped fuse body 16 to cause electrode-migration, and thereby the fuse body 16 is blown to open. The size of the cathode is relatively large because it needs to provide an enough place for the plurality of the tungsten contacts to land thereon to totally provide a large electron flow. In turn, it needs a large blowing device (i.e. a MOS transistor) to provide the adequate electron flow since a large electron flow is required to blow the fuse body. Accordingly, it is difficult for a conventional poly efuse with such a big size to be utilized in a 32 nm semiconductor node. Moreover, in a 32 nm manufacturing process, the conventional poly gate would be replaced by a metal gate. As a result, the manufacturing process of the conventional poly efuse would not be conveniently integrated with the 32 nm manufacturing process.
Therefore, there is still a need for a novel efuse structure having a relatively small size, which may be further conveniently made from metal gate material.